(1) Field of the Invention
The invention relates to the field of apparatuses intended for local hyperthermia therapies. The invention also relates to a method of using apparatus of this sort.
(2) Description of Related Art
Local hyperthermia therapies consist in heating, locally, a target zone of biological tissue. When this type of therapy is used in the context of gene therapy, the heat may, for example, be used for its action on a heat-sensitive promoter. Heat may also be used to necrose biological tissue and to ablate tumors.
Also, local hyperthermia therapies offer numerous advantages. These advantages are both qualitative and economic. From the qualitative point of view, they offer, for example, strong potential for the control of treatments such as gene therapies, the local application of medications, the ablation of tumors, etc. From the economical point of view, they are compatible with the ambulatory treatment of patients, they make it possible to reduce the length of time spent in hospital, etc.
In hyperthermia therapies, the heat may, for example, be provided by a laser, microwaves or radio-frequency waves, focused ultrasound, etc. In general, local hyperthermia therapies allow medical operations where the invasive nature is reduced to the minimum. However, among the aforementioned energy types, focused ultrasound is particularly beneficial since it makes it possible to heat the focusing zone, in a noninvasive way, deep within a biological body, without significantly heating the tissue in the vicinity of the focusing zone.
In all cases, the temperature of the target zone and of its immediate surroundings, during the treatment, must be accurately and continuously controlled, although the supply of energy is localized and fast, of short duration (of the order of a few seconds). To this end, it is possible to fit temperature probes in the target zone and its immediate surroundings. However, it is also possible to use Magnetic Resonance Imaging (MRI). This is because MRI makes it possible to obtain an accurate map of the temperature distributions and detailed anatomical information. Furthermore, MRI allows noninvasive control of the temperature.
Devices for controlling the temperature during treatments by focused ultrasound are already known, based on magnetic resonance thermometry. Devices of this sort are in particular described in the following documents: xe2x80x9cControl system for an MRI compatible intracavitary ultrasonic array for thermal treatment of prostate diseasexe2x80x9d, Smith NB et al., Proceedings of the annual meeting of the International Society of Magnetic Resonance in Medicine, 1999, p. 672 and xe2x80x9cReal time control of focused ultrasound heating based on rapid MR thermometryxe2x80x9d, Vimeaux FC et al., Invest. Radiol. 1999, 34, p. 190-193. In the devices described in these documents, the retrocontrol of the heat provided by the focused ultrasound, by virtue of the maps obtained by MRI, is of the PID (Proportional Integral and Derivative) type. Furthermore, with these devices, control of the heat supplied to the tissue is based on taking into account a temperature measured in the focusing zone of the ultrasound equipment, or corresponding to a mean obtained from the spatial temperature distribution in the mapped zone.
FIG. 1 shows the temporal change in the mean temperature of the focusing zone, processed by virtue of the device described in the first of these documents. In this figure, the temperature increases up to a plateau corresponding to the temperature that it is desired to reach in the focusing zone. It may be noted that the temperature desired in the focusing zone is reached only after a period of about 30 minutes.
FIG. 2 shows the temporal change in the mean temperature in the focusing zone, processed by virtue of the device described in the second of the documents mentioned above. It may be noticed that the temperature desired in the focusing zone is reached in less than 2 minutes. However, variations in the desired temperature, of plus or minus 4xc2x0 C., are observed.
One aim of the invention is to provide equipment for the heat treatment of a target zone of biological tissue, enabling the temperature desired in the target zone to be obtained quickly and at the same time the temperature in this target zone to be maintained and controlled with increased accuracy, compared to that which was possible with the techniques of the prior art.
This aim is achieved, according to the invention, by virtue of equipment for the heat treatment of a target zone of biological tissue, comprising:
energy generating means for supplying energy locally in the target zone;
means for measuring and recording the temperature in the target zone;
a control unit comprising means for determining, from the temperature measured in the target zone, the amount of energy having to be supplied to the target zone, and means for controlling the energy generating means to deliver this power value;
characterized in that the control unit furthermore comprises means of numerically processing, point by point, the spatial temperature distribution in the target zone and its surroundings, in order to calculate temperature gradients.
The heat treatment equipment according to the present invention takes into account the actual spatial temperature distribution in the target zone, but also in the surroundings of this zone. That is to say that it takes into account and processes, point by point, this spatial distribution. Unlike the heat treatment equipment of the prior art, the spatial temperature distribution is used to deduce therefrom temperature gradients and not merely averages. This makes it possible to estimate, with increased accuracy, the amount of energy which must be applied and therefore to achieve the desired temperature more quickly and to maintain the temperature of the biological tissue with greater stability.
Advantageously, the control unit of the heat treatment equipment according to the invention furthermore comprises means for estimating the local heat energy losses, from an estimate of the heat conduction and of the spatial temperature distribution in the target zone and its surroundings. This is because the information supplied by the value of the temperature gradients and the taking into account of an estimate of the local heat losses not only make it possible to understand the way in which the treated biological tissue has reacted to the heat already applied thereto, but furthermore, make it possible, by virtue of the prediction concerning the way in which the biological tissue will react to the heat. This also makes it possible to make the temperature of the heat-treated tissue change more quickly toward the desired temperature and to maintain the temperature of the biological tissue with greater stability.
Advantageously, the energy generating means of the heat treatment equipment according to the invention emit focused ultrasound. This is because focused ultrasound makes it possible to supply heat to a very localized zone, in a noninvasive manner, even if this zone is located deep within a human body or an animal. Furthermore, the focusing makes it possible for the tissue near to the zone of treated biological tissue not to be significantly heated.
Advantageously, the means for measuring and recording the spatial temperature distribution of the heat treatment equipment according to the invention comprise a magnetic resonance imaging apparatus. This is because MRI allows measurement of the temperature, which is noninvasive, accurate and well resolved in many points of the mapped zone. The data collected by MRI are, furthermore, easily processed numerically.
Advantageously, the heat treatment equipment according to the invention comprises means for evaluating the spatial distribution, in the target zone and its surroundings, of the energy supplied to the target zone.
According to another aspect, the invention is a method for regulating equipment for heat treating a target zone of biological tissue, comprising the step consisting in locally applying energy to the target zone, characterized in that it further comprises the steps consisting in
evaluating the temperature gradients in the target zone and its surroundings; and
thereby deducing the energy to be applied to the target zone in order to reach the desired temperature.
Advantageously, this method furthermore then comprises the step consisting of estimating the local energy losses, in the target zone and its surroundings.
Advantageously, this method furthermore comprises the step consisting of evaluating the spatial distribution, in the target zone and its surroundings, of the energy supplied to the target zone.
Other aspects, aims and advantages of the invention will become more clearly apparent on reading the following detailed description.